feat: enhance receipt import functionality with category selection and PDF opening support

flutter/lib/core/ui/category_then_product_picker.dart

@@ -13,6 +13,20 @@ import '../../features/admin/domain/admin_category_node.dart';
 class CategoryThenProductPicker {
   CategoryThenProductPicker._();
 
+  static List<String>? _findPath(
+    List<AdminCategoryNode> nodes,
+    int id,
+    List<String> parents,
+  ) {
+    for (final node in nodes) {
+      final path = [...parents, node.name];
+      if (node.id == id) return path;
+      final found = _findPath(node.children, id, path);
+      if (found != null) return found;
+    }
+    return null;
+  }
+
   /// Samlar alla ID:n för [node] och alla dess ättlingar rekursivt.
   static Set<int> _collectIds(AdminCategoryNode node) {
     final ids = <int>{node.id};
@@ -74,7 +88,7 @@ class CategoryThenProductPicker {
     }
 
     // Samla alla kategori-IDs i den valda grenen (inkl. ättlingar)
-    final categoryIds = _collectIds(selectedCategory!);
+    final categoryIds = _collectIds(selectedCategory);
 
     // Filtrera produkter på dessa kategorier
     final filtered = products
@@ -93,12 +107,39 @@ class CategoryThenProductPicker {
       context,
       products: useList,
       value: currentProductId,
-      label: 'Produkt i "${selectedCategory!.name}"',
+      label: 'Produkt i "${selectedCategory.name}"',
       categoryFilter: null, // redan förfiltrerat
       initialQuery: initialQuery,
       onCreate: onCreateBound,
     );
   }
+
+  static Future<({int id, String name, String path})?> showCategorySheet(
+    BuildContext context, {
+    required List<AdminCategoryNode> categoryTree,
+    int? preselectedCategoryId,
+  }) async {
+    if (!context.mounted) return null;
+    final selectedCategory = await showModalBottomSheet<AdminCategoryNode>(
+      context: context,
+      isScrollControlled: true,
+      useSafeArea: true,
+      builder: (ctx) => _CategoryPickerSheet(
+        tree: categoryTree,
+        preselectedId: preselectedCategoryId,
+        onSelected: (node) => Navigator.pop(ctx, node),
+      ),
+    );
+    if (selectedCategory == null) return null;
+    final path = _findPath(categoryTree, selectedCategory.id, const [])
+            ?.join(' > ') ??
+        selectedCategory.name;
+    return (
+      id: selectedCategory.id,
+      name: selectedCategory.name,
+      path: path,
+    );
+  }
 }
 
 // ── Kategoriträdets bottenark ────────────────────────────────────────────────
@@ -293,7 +334,7 @@ class _CategoryTileState extends State<_CategoryTile> {
           dense: true,
           selected: isPreselected,
           selectedColor: theme.colorScheme.primary,
-          selectedTileColor: theme.colorScheme.primaryContainer.withOpacity(0.3),
+          selectedTileColor: theme.colorScheme.primaryContainer.withValues(alpha: 0.3),
           leading: Icon(
             Icons.label_outline,
             size: 16,